1. Field of the Invention
The present invention relates to a high-pressure pump for an internal combustion engine (hereinafter referred to as an “engine”).
2. Description of Related Art
Conventionally, a fuel supply apparatus for supplying fuel to an engine includes a high-pressure pump that pumps high pressure fuel. A fuel rail connected with injectors stores high pressure fuel pumped by the high-pressure pump. By keeping pressure in the fuel rail, fuel is injected through the injectors.
However, for example, due to the failure of a metering valve of the high-pressure pump, pressure in the fuel rail may sometimes become abnormally high so that the pressure in the fuel rail exceeds an allowable range. As a result, the fuel rail or the injectors may be damaged disadvantageously. In order to deal with the above disadvantage, there has been proposed a high-pressure pump having a pressure relief valve that is opened when the pressure in the fuel rail becomes abnormally high.
Even when the pressure in the fuel rail becomes a predetermined pressure that exceeds the allowable range, the above pressure relief valve is capable of reducing pressure in the fuel rail. When the pressure in the fuel rail stays within the allowable range, the pressure relief valve is not operated. However, even when the pressure in the fuel rail stays within the allowable range, the pressure in the fuel rail may not be within an appropriate range, for example. In the above case, when the engine stops, the injector may cause the fuel leakage into the cylinder, or a fuel injection quantity may be larger than necessary disadvantageously. Also, fuel vapor may occur in the fuel rail disadvantageously.
Therefore, there is further proposed a high-pressure pump that includes the pressure relief valve and also a constant residual pressure valve that is configured to maintain the fuel pressure in the fuel rail in an appropriate condition. In the above high-pressure pump, the constant residual pressure valve is provided within a valve element of the pressure relief valve (see, for example, JP-A-S60-119366). For example, the constant residual pressure valve is a ball valve, and thereby the high-pressure pump is reduced in size.
However, in JP-A-S60-119366, when the constant residual pressure valve is opened, oil tightness between the constant residual pressure valve and the oil valve seat may not be sufficiently achieved. More specifically, when an opening/closing body 32 shown in FIG. 2 of JP-A-S60-119366 opens the valve passage, vortex flow is generated at a position around the opening/closing body 32 or downstream of a spring receiver 34. As a result, the opening/closing body 32 becomes unstable because of the above generated vortex flow. Thus, the opening/closing body 32 tends to be engaged with a valve seat at a position slightly different from a suitable position, at which the opening/closing body 32 closes the valve appropriately. In general, a biasing force for closing the constant residual pressure valve is not sufficiently large. As a result, the slightly different position of the opening/closing body 32 may cause the insufficient oil tightness. Also, in the configuration of JP-A-S60-119366, the machining is difficult, and the manufacturing cost may be increased.